This invention concerns an improved start-up procedure for a processing unit. More particularly, the procedure concerns an upflow, ebullated bed reactor for the hydroprocessing of heavy hydrocarbon residues. The utility of the invention lies in an improved method of operating a hydroprocessing reactor, especially during start-up and shut-down periods.
Prior art methods of start-up procedures for ebullated bed, heavy hydrocarbon residue processing units are exemplified by U.S. Pat. Nos. 3,244,617 (Galbreath), 3,491,017 (Rapp), and 3,491,018 (Schuman). The first of these procedures tries to control the rate of conversion, or hydrogenation, during start-up by controlling the temperature and residence time in the reactor in order to minimize external heat input, thereby reducing construction costs and operating expenses. The latter procedures, respectively, control conversion to less than about 40 vol.% until about 3 bbl. of heavy feedstock/lb. new catalyst have been processed, by reactor temperature control to present premature deactivation of the catalyst, and by increasing the reactor temperature and space velocity to promote a constant conversion rate of at least 75 vol.%.
Broadly, a typical start-up procedure for the hydroprocessing of heavy hydrocarbon residue in an upflow, ebullated bed reactor comprises:
Blowing hot gas through a charge of catalyst in the reactor, to heat the reactor and contents. This takes about 24-48 hours. PA1 Adding a light gas oil of about 350.degree.-750.degree. F. boiling range. This step forms and maintains an ebullated bed and takes about 4-24 hours. PA1 Phasing in the heavy hydrocarbon residue, while maintaining the top of the catalyst bed at a relatively constant height while heating the reactor inventory. This takes 8-24 hours. PA1 Establishing final operating parameters.
It is noted that this typical procedure is modified for times, rates, temperatures, etc. for different feedstocks, with these modifications being known or calculated from previous runs or from pilot plant studies.